1. Field of Invention
The invention relates to a an S-type smooth command generating method and, in particular, to an S-type smooth command generating method used in a servo module with a servo driver and motor.
2. Related Art
Because of abrupt changes in the input commands, the servo motor or servo module may have large jumps (proportional to the derivative of acceleration) during motion control. This results in vibrations and noises of the mechanical structure. This phenomenon is caused by the large instantaneous current from the servo module. Vibrations do not only affect the machining precision, the servo module lifetime will also be shortened after being exposed in such an operating environment for a long time.
The purpose of the S-type smooth commands is mainly to process motion commands smoothly during the operation of the motor. In reality, different control structures have been developed to satisfy constraints in different fields. For example, the motion controller uses a floating calculator with high-speed computing ability and high resolution to construct a complicated and complete command processing unit.
There are several methods to generate velocity smoothing commands. One method is to process the acceleration trapezoid curve using a low-pass filter, generating an approximately S-type smooth command. Another method is to average-filter the acceleration trapezoid curve for appropriate rectification, also generating an approximately S-type smooth command. A further method provides an S-type curve ratio that selects an appropriate output level according to needs. However, it is less flexible.
Generating S-type smooth commands encounters some technical problems to overcome. For example, in the analog velocity mode, the rotational velocity of the motor should remain fixed when the input voltage commands are the same. However, the rotational velocity changes with the adjustment in the acceleration/deceleration time.